Cordierite composition and method of production

ABSTRACT

A Group IIA metal-Group IIIA metal-silicon substantially homogeneous liquid alkoxide is prepared from a reaction mixture of a Group IIA metal, a Group IIIA metal, a silicon tetraalkoxide, and a liquid defined by the formula ROR&#39; where R is an alkyl group and R&#39; is hydrogen or an alkyl group. The alkoxide can then be hydrolyzed, azeotropically distilled, dried, milled, and calcined to produce a ceramic powder. Advantageously, the ceramic powder can be compacted and sintered at relatively low temperatures which enable it to be used in electrical applications where high sintering temperatures would be deleterious.

This application is a continuation of prior U.S. application Ser. No.911,221, filed 9/24/86, now U.S. Pat. No. 4,835,298.

BACKGROUND OF THE INVENTION

Alumina, mullite, and other refractory ceramics have been used for sometime as substrates for printed circuits having conduction patterns madefrom inks or pastes containing tungsten, molybdenum, gold, silver, orcopper powders, terminal pads to attach semiconductor chips, connectingleads, capacitors, resistors, covers, and vias (i.e. holes filled withmetal paste) to connect different layers of conductive patterns. Aluminais preferable due to its excellent electrical insulating properties,thermal conductivity, stability, and strength. However, this materialhas some disadvantages including signal propagation delay and noise inhigh performance applications, restriction of the type of the conductivemetals due to alumina's high maturation temperature, and a high thermalexpansion coefficient.

As an alternative to alumina, U.S. Pat. No. 2,920,971 to Stookeydiscloses the use of glass ceramics with dielectric properties and highmechanical strengths. Stookey's glass ceramics are characterized as"bulk-crystallized" or "bulk" glass ceramics as opposed to sinteredglass ceramics. Bulk glass ceramics are generally inferior to sinteredglass ceramics due to the latter's high flexural strength.

Although sintered glass ceramics are well known, they are generallyunsuitable as substrates for printed circuits, because many glassceramics can only be sintered at temperatures well in excess of 1000° C.Such temperatures are above the melting point of the gold (having amelting point of 1064° C.), silver (962° C.), and copper (1083° C.)conductors within the printed circuit.

U.S. Pat. No. 4,587,067 to Agrawal et al. discloses a method ofmanufacturing low thermal expansion-modified cordierite compositions.The process comprises: Blending MgO, Al₂ O₃, SiO₂, and GeO₂ ;Homogenizing the blended material by wet ball milling; Oven drying;Comminuting; Cold compacting; Sintering; and Consolidation to fulldensity. Sintering is carried out at about 1350° C.

One way of sintering below 1000° C. is by treating the glass powder withan alkali solution and then sintering under vacuum, as taught byHelgesson, Science of Ceramics, British Ceramic Society, 1976, pp.347-361. Another technique of sintering below 1000° C. is to use glasscompositions which are unsuitable as substrates for printed circuits dueto their relatively high fluidity. This fluidity causes movement of thesubstrate's conduction patterns when sintering these materials.

U.S. Pat. No. 4,413,061 to Kumar, et al., ("Kumar") seeks to overcomethe above-noted problems with respect to sintered glass ceramics bycrystallizing the glass ceramics during sintering so that a rigidnetwork of crystallites are formed. These crystallites reduce thefluidity of the substrate, thereby permitting greater dimensional anddistortional control. Cordierite (2MgO.2Al₂ O₃.5SiO₂) glass ceramicsaccording to Kumar are prepared by melting a mixture of Al₂ O₃, MgO,SiO₂, and other materials, quenching the molten glass by pouring it intocold water to produce a cullet, grinding the cullet, mixing the groundcullet with a binder, casting the mixture into sheets, placingconductive patterns on the sheets, laminating, and sintering usually attemperatures of at least 925° C. (see Table III). As to one example(i.e. Example 10), sintering temperatures as low as 870° C. areindicated to be satisfactory. The resulting cordierite is primarily inthe μ or α phases or mixtures thereof. Although Kumar producescordierite, the grains of this cordierite are not homogenous. Kumar alsorequires a very high temperature glass melting step and a fairly hightemperature sintering step. Moreover, it is difficult to achieve uniformfiber reinforcement when the fibers are mixed with Kumar's ceramicpowder prior to sintering.

Ceramic materials have been formed from alkoxides. However, it has notbeen possible to manufacture certain ceramic compositions from ahomogeneous liquid magnesium-aluminum-silicon alkoxide in a singlereactor, because the magnesium alkoxides are generally insoluble incommon organic solvents. Even if each of the alkoxides are separatelyformed and then mixed, a uniform distribution cannot be achieved due tomagnesium's insolubility.

U.S. Pat. Nos. 4,242,271 and 4,288,410 to Weber, Hill, and Weeks preparealuminum alkoxides by reacting impure aluminum with a stoichiometricexcess of monohydric alcohol.

U.S. Pat. No. 3,761,500 to Thomas ("Thomas") discloses a magnesium,aluminum double alkoxide and the process of preparing it according tothe following non-catalytic reaction:

    Mg+2Al(OR).sub.3 +2 ROH⃡Mg[Al(OR).sub.4 ].sub.2 +H.sub.2 +MgAl.sub.2 (OR).sub.8

where the OR group is an alkoxy group of 4-7 carbon atoms. Thomas'process involves the reaction of two equivalents of aluminum alkoxidewith one equivalent of magnesium. Consequently, the composition of thefinal product is limited to a ratio of magnesium to aluminum of 1 to 2.The double alkoxides can be used to form ultra high purity spinel byhydrolyzing the double alkoxide with water and then calcining or firingthe hydrolysis product (col. 2, lines 33-41). The product of thisprocess is useful as a refractory material.

U.S. Pat. No. 3,791,808 to Thomas relates to a process of preparing athermally crystallizable oxide product by hydrolyzing a siliconalkoxide, reacting the hydrolyzed product with a metal alkoxide, anaqueous metal solution, or water to produce a gel, and heating toproduce a thermally crystallized product. The thermally crystallizedproduct is preferably a particulate mass with a particle size less thanabout 0.2 micron which can be treated to produce either a dense orporous body. Although any metal is said to be suitable in the metaloxide component, magnesium cannot be used in the alkoxide form, becausesuch alkoxides are not suitably soluble. The products disclosed by U.S.Pat. No. 3,791,808 are useful in heat exchangers, dinnerware, andfilters.

U.S. Pat. No. 4,052,428 to Lerner, et al., relates to the preparation ofstable aluminum alkoxide solutions by reacting aluminum metal with amixture of isobutyl alcohol and n-butyl alcohol. The resulting alkoxideis useful in forming catalysts and paint additives.

U.S. Pat. No. 4,266,978 to Prochazka discloses a non-aqueous gel of atleast two metal oxides which are prepared by reacting a metal alkoxidewith a metal halide and heating the reaction product. The gel iscalcined at a temperature from 600° C. to about 1300° C. to produce aglassy or crystalline submicroscopically homogeneous mixture of theoxides.

U.S. Pat. No. 4,422,965 to Chickering, et al., discloses a process forcontaining a solution of nuclear waste in borosilicate glass. The glassprecursor is prepared from a mixture of alkoxides which are hydrolyzedand then polymerized into an organic-free oxide network.

U.S. Pat. No. 4,430,257 to Pope, et al., relates to a method ofcontaining nuclear waste in a glass forming composition prepared fromtetraethylorthosilicate (TEOS), an aluminum alkoxide, or amagnesium-aluminum alkoxide in a 1 to 2 ratio, a boron alkoxide or acalcium alkoxide, an alcohol, and a sodium compound. Once thecomposition components are intimately mixed, excess alcohol and waterare boiled off as an azeotrope to leave a homogeneous colloidal glassforming composition.

SUMMARY OF THE INVENTION

In accordance with the present invention, at least one Group IIA metal(i.e. beryllium, magnesium, calcium, strontium, barium, and radium), atleast one Group IIIA metal (i.e. aluminum, gallium, indium, andthallium), and at least one silicon tetraalkoxide (e.g.tetraethylorthosilicate, tetramethylsilicate) are used to produce aGroup IIA metal-Group IIIA metal-silicon mixed liquid alkoxide which isconverted to a ceramic powder and can then be compacted and sintered. Ina preferred embodiment, the compacted and sintered ceramic powder iscordierite, the Group IIA metal is magnesium, the Group IIIA metal isaluminum, the silicon tetraalkoxide is tetraethylorthosilicate, and theGroup IIA metal-Group IIIA metal-silicon mixed liquid alkoxide ismagnesium-aluminum-silicon ethoxide.

A homogeneous, soluble, liquid alkoxide is prepared by reacting amixture of at least one silicon tetraalkoxide, at least one Group IIAmetal, and at least one Group IIIA metal with a liquid defined by theformula ROR' where R is an alkyl group and R' is hydrogen or an alkylgroup. R is preferably a lower alkyl group with 1 to 3 carbon atoms,while R' is preferably hydrogen. The liquid defined by the formula ROR'can be, inter alia, an alcohol or an ether provided that the liquid willremain a liquid under alkoxide synthesis conditions (i.e. pressure andtemperatures). As noted the preferred alkoxide, ismagnesium-aluminum-silicon liquid ethoxide which results when the liquiddefined by the formula ROR' is ethanol. When ethanol is utilized, itsreaction with the metals results in the generation of hydrogen whereasno gas is generated by the reaction if an ether is used instead.

The silicon tetraalkoxide can be formed from any lower alkyl group withalkyl groups of 1 to 3 carbon atoms being most preferred. It isparticularly preferred that the liquid defined by the formula ROR' andthe silicon tetraalkoxide have the same ligand. In the preferredembodiment, this is achieved by utilizing tetraethylorthosilicate as thesilicon tetraalkoxide and by using ethanol as the liquid defined by theformula ROR'.

During the reaction of the Group IIA metal, the Group IIIA metal, andthe silicon tetraalkoxide, less than the stoichiometric amount of liquiddefined by the formula ROR' is initially used and additional quantitiesof this liquid are periodically added to the reaction mixture to controlthe reaction rate, and such addition is continued until the reaction iscompleted. When the liquid defined by the formula ROR' is ethanol, thisliquid is added when the reaction's rate of hydrogen generation ceasesor substantially ceases. The reaction mixture can optionally contain arate enhancement agent in an amount effective to increase the rate ofalkoxide synthesis. One example of a suitable rate enhancement agent isany alkoxylation catalyst such as, molecular halogens, metal halides,and mixtures thereof. Preferably, the rate enhancement agent ismolecular iodine in an amount of 5.5×10⁻⁴ to 1.3×10⁻³ moles per mole ofGroup IIA metal.

One alternative embodiment is to replace all or part of the at least oneGroup IIA metal with at least one Group IA metal (i.e. lithium, sodium,potassium, rubidium, cesium, and francium). It is believed that themagnesium and aluminum in the alkoxide are not merely present as a blendof magnesium alkoxide and aluminum alkoxide, but they are insteadcomplexed during the alkoxylation step. This complex is thought to becarried through to the compacted and sintered cordierite to give it andall the intermediate materials formed by the reaction improvedproperties. The complex in its alkoxide form is believed to be ahomopolar alkoxide of Mg(OR)₂ and Al(OR)₃ as follows: ##STR1## wherein Ris an alkyl group. It is when this homopolar alkoxide is formed thatmagnesium is soluble in ethanol containing aluminum and silicontetraalkoxide. Such homopolar alkoxide formation may be achieved whenthe molar ratio of magnesium to aluminum in the mixed liquid alkoxide isbetween 7.0 to 1 and 0.2 to 1. Thus, molar ratios of magnesium toaluminum of over 1 to 2 which could not be achieved by prior artprocesses can now be produced.

The mixed liquid alkoxide can be reacted to produce a sinterable,ceramic powder by treating the Group IIA metal-Group IIIA-metal-siliconmixed liquid alkoxide under conditions which produce a hydrated GroupIIA metal-Group IIIA metal-silicon mixed oxide and drying the hydratedGroup IIA metal-Group IIIA metal-silicon mixed oxide. In the preferredembodiment, the hydrated Group IIA metal-Group IIIA metal-silicon mixedoxide is hydrated magnesium-aluminum-silicon mixed oxide. After thishydrated metal mixed oxide is dried, it can be milled by ball or jetmilling. Alternatively, the material can be wet milled in ethanol orwater and then dried.

The step of treating the mixed liquid alkoxide to produce a hydrotreatedGroup IIA metal-Group IIIA metal-silicon mixed liquid oxide ispreferably carried out by hydrolyzing the Group IIA metal-Group IIIAmetal-silicon mixed liquid alkoxide. Prior to hydrolyzing, the alkoxideis optionally first diluted with ethanol. A solution of water andethanol is then added to effect hydrolysis. The water is preferablydiluted with ethanol at a 1:12 to 1:6 weight ratio of water to ethanol.These ratios can be varied to control the rate of oxide formation.Specifically, hydrolysis rates are increased by high ratios of water toethanol and decreased by low ratios of water to ethanol. A fast rate offormation will increase the tendency to yield a dense oxide with manyphases in the sintered product, while a slow rate of formation tends toproduce a homogeneous oxide with one phase in the sintered product.

Hydrolyzing results in the formation of a product which may be a sol.When permitted to stand, a gel is formed. After gelation, the gel isoptionally quiescently aged for a time sufficient to effect substantialpolymerization and to complete hydrolysis. Useful polymerizationgenerally occurs in anywhere between 10 seconds and 24 hours, dependingupon (amongst other things) the concentration of water. Afterquiescently aging, water is optionally added to the gel, and the gelmixed with water is agitated to shear the gel and break it up into smallparticles. This agitation and continued hydrolysis may be attemperatures up to 80° C. for up to 5 days depending on temperature anddilution. After shearing, alcohol produced from the hydrolyzing step isoptionally separated from the hydrated Group IIA metal-Group IIIAmetal-silicon oxide by azeotropic distillation. The alcohol removed byazeotropic distillation can be further distilled to remove any water andthen recycled to the alkoxylation reaction or to the hydrolysisreaction. Such recycling makes the process more economical by reducingthe quantity of new ethanol added to the alkoxylation and hydrolysisreactions. In addition, the waste treatment requirements of the processare eliminated. The azeotropic distillation step is, however, optional,because the subsequent step of drying can be used to effect alcoholremoval in addition to the removal of water.

It is often desirable to dope the ceramic powder with boron to aidsintering. One way of achieving this result is by blending a solution ofboric acid crystals and alcohol with the mixed liquid alkoxide prior tohydrolyzing. The ceramic powder can also be doped with phosphorus topromote nucleation and to regulate microstructural development. One wayto effect such doping with phosphorus is by adding a solution ofphosphoric acid, water, and ethanol to the liquid alkoxide prior tohydrolyzing. In addition, lithium, titanium, tin, and zirconium oxidessimilarly can be used to dope the resultant ceramic powder, therebypromoting nucleation or sintering.

After drying and milling, the hydrated Group IIA metal-Group IIIAmetal-silicon mixed metal oxide can be calcined (i.e. dehydroxylated) toform a Group IIA metal-Group IIIA metal-silicon mixed metal oxide. Inthe preferred embodiment, one way to effect calcination is by warmingthe hydrated magnesium-aluminum-silicon mixed metal oxide to 600°-800°C. One preferred calcination temperature schedule comprises warming thehydrated Group IIA metal-Group IIIA metal-silicon oxide from roomtemperature to 100° C. over the course of an hour, maintaining thetemperature at 100° C. for one hour, heating from 100° C. to 700°-750°C. at a rate of 100° C. per hour, and cooling.

After calcining, the Group IIA metal-Group IIIA metal-silicon mixedmetal oxide can be milled by dry ball milling, wet ball milling inethanol, or jet milling to reduce the particle size of the mixed metaloxide.

In the preferred embodiment, the product of calcination is anagglomerate of adhered, uniformly sized, amorphous primary particles ofmagnesium-aluminum-silicon oxides. The agglomerate has a uniform,homogeneous composition as a result of being ultimately formed from ahomogeneous liquid solution and is generally friable to permit millingby any suitable means, (such as those disclosed in the previousparagraph) to a smaller size and a more uniform size distribution thanthe cullet of Kumar. When doped with boron or phosphorus, the primaryparticles may contain oxides of boron and phosphorus. Each of theagglomerates typically has a size ranging from 1 to 50 microns.

After optional calcination, the Group IIA-Group IIIA-silicon mixed oxidepowder is milled to render it capable of being compacted and sintered tosubstantially full density. Sintering causes crystallization of theamorphous primary particles. The threshold sintering temperature is anindication of the homogeneity and consistency of the grains of mixedmetal oxides. In the present invention, the magnesium-aluminum-siliconmixed oxide is uniform to the extent that it can be sintered attemperatures less than 925° C., preferably less than 900° C., morepreferably less than 875° C., and most preferably at 850° C. which isbelow the threshold sintering temperatures of Kumar.

By controlling the composition of magnesium, aluminum, and silicon inthe oxide, crystalline cordierite ceramics are produced duringsintering. Preferably, the oxide contains 10-40% by weight magnesium,15-40% by weight aluminum, and 40-75% by weight silicon. The compositionlimits are set on the one hand by the need to ensure that cordieriteappears as the major crystalline phase in order to achieve desiredthermal expansion coefficients and, on the other hand, to facilitatesintering at low temperatures. If boron or phosphorus doping agents wereused, the cordierite also will include oxides of boron and phosphorus,respectively.

While not wishing to be bound by theory, it is believed that the easewith which the agglomerate produced by calcination is ground to asmaller size than that of Kumar's glass cullet, and the ability of theground agglomerate to be sintered at lower temperatures than in Kumar'sprocess results from the preceeding steps of the present process.Specifically, it is believed that the ease of grinding occurs as aresult of the agglomerates being made up of small primary particles. Inaddition, it may be possible to produce unagglomerated particles. Theability to sinter at low temperatures is achieved due to the high degreeof homogeneity resulting from polymerization which occurs during gellingand aging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram depicting the process of the present inventionaccording to the preferred embodiment.

FIG. 2 is a schematic diagram of a commercial version of the presentinvention according to the preferred embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing the process of the present inventionaccording to the preferred embodiment for manufacturing cordierite. Inthis process, magnesium A, aluminum C, tetraethylorthosilicate E, andethanol D undergo an ethoxide formation reaction 2 in the presence of aniodine initiator B. The ethoxide formation reaction 2 generates hydrogengas F and a magnesium-aluminum-silicon mixed liquid ethoxide G which canbe either stored 3 or mixed 4 with ethanol E. Boric acid crystals inethanol H can optionally be added to the mixture of ethanol and themagnesium-aluminum-silicon mixed liquid ethoxide before the mixtureundergoes hydrolysis 6. Hydrolysis 6 is effected by adding a mixture ofethanol I, water J, and optionally phosphoric acid K, all of which haveundergone blending 8. Hydrolysis 6 results in the formation of a gel Kwhich is subjected to quiescent aging 10 to effect furtherpolymerization. The aged gel L is then subjected to shearing 12 to breakit into a slurry of small particles M, followed by azeotropicdistillation 14 which separates ethanol E from the remaining slurry N.The ethanol separated by azeotropic distillation can be recycled toeither the mixing step 4 or the ethoxide formation step 2 after dryingin alcohol-water separator 13. The slurry N then undergoes optionaladditional agitation to effect complete hydrolysis 16. The aged gel O isthen either subjected to drying 18 which removes water and residualethanol P or wet milling 20 in the presence of ethanol or water O. Afterwet milling 20, the milled material R is subjected to drying 18. Thedried, hydrated magnesium-aluminum-silicon mixed oxide S can thenundergo ball or jet milling 22 followed by calcining 24 to convert thehydrated magnesium-aluminum-silicon mixed oxide to agglomeratedmagnesium-aluminum-silicon mixed oxide T. The calcined material T thencan undergo either dry ball or jet milling 26 or wet milling 28 inethanol or water U. The milled material V can then be compacted andsintered to produce dense ceramic parts W.

FIG. 2 is a schematic diagram of a commercial version of the presentinvention according to the preferred embodiment. In accordance with thisembodiment, alcohol and tetraethylorthosilicate are weighed in alcoholweigh tank 102 and tetraethylorthosilicate weigh tank 104, respectively.Materials from these weigh tanks are charged into alkoxide reactor 108.Magnesium and aluminum are charged to this reactor by screw conveyor106. In alkoxide reactor 108, the reactants are agitated by mixer 110and heated by steam jacket 112 surrounding the reactor. Nitrogen fromnitrogen source 109 is also added to the alkoxide reactor to preventformation of an explosive atmosphere during initial charging ofreactants. Condenser 114 removes any condensible materials from thevapors leaving the alkoxide reactor 108, so that only non-condensibles(e.g. hydrogen) are withdrawn.

After the alkoxide reaction is completed, the product is withdrawn fromthe bottom of the alkoxide reactor 108 and charged to hydrolysis reactor116. Alcohol mixed with water and mineral acid in weigh tank 118 is alsocharged to hydrolysis reactor 116. The material in this reactor isagitated with mixer 120 and heated by steam jacket 122 to effecthydrolysis. Nitrogen is also added to hydrolysis reactor 116 to preventexplosions. Vapors are removed from the reactor and passed throughcondenser 126 to return condensible materials to the hydrolysis reactor.

When hydrolysis is completed, the product remains in the hydrolysisreactor 116 to permit quiescent aging and shearing with mixer 120.

After aging and shearing, the material in the hydrolysis reactor 116 ischarged to stripper 128 where this material is agitated by mixer 130 andheated by reboiler 136. Nitrogen from nitrogen source 132 and water fromwater source 134 are added to the stripper to prevent explosions and toprovide water for stripping, respectively. Vapors generated in thestripper 128 are withdrawn and passed through azeotropic distillationcolumn 138. Such azeotropic distillation conventionally requires morethan one distillation column. Consequently, column 138 represents theplurality of columns needed to effect such azeotropic distillation. Theoverhead product is passed through condenser 140 to an alcohol recoverysystem. The bottom product from distillation column 138 is recycled tostripper 128.

The material withdrawn from the bottom of stripper 128 (i.e. hydratedmagnesium-aluminum-silicon mixed metal oxide) is charged to spray dryer142.

The spray dried hydrated magnesium-aluminum-silicon mixed metal oxide ispassed to filter bag house 144 from which gas is exhausted. The solidmaterial retained by the filter bag house 144 is passed to rotarycalciner 146 where a magnesium-aluminum-silicon mixed metal oxideagglomerate is produced.

The calcined material is ground in jet mill 148 and conveyed to filterbag house 150. Gas is exhausted from the filter bag house 150, while theretained material is put in drums at product drumming unit 152 forsubsequent compaction, sintering, and use.

EXAMPLE 1

For this alkoxide synthesis, a reactor made from a 22 liter glass flaskis used. The flask has 3 openings to receive a thermometer and a mixerand to discharge gas produced during the alkoxide synthesis. The openingfor discharging gas is provided with a condenser to return condensiblesto the reactor and is followed by a gas meter to measure the volume ofnon-condensible gas produced. The opening for the thermometer has abranch through which reactants can be added to the flask. A resistanceheater is positioned beneath the reaction flask to warm the contents ofthe flask.

In the reaction flask, the following reactants are mixed: 5.556kilograms of tetraethylorthosilicate, 349.62 grams of aluminum metal,382.74 grams of magnesium metal, 2.99 grams of iodine, and 450 grams ofethanol. The heater is then turned on to warm the reactants. Thereactants are heated to 70° C. An exothermic reaction between thealcohol and metals occurs, causing the temperature to rise to theboiling point of the liquid reactants, which is approximately 78° C.Once the reaction is near completion, the flask contents are allowed tocool, at which time additional alcohol is added to permit furtherreaction with the remaining metal. This periodic alcohol addition isperformed according to the schedule set forth below in Table 1. Periodicalcohol addition in less than stoichiometric quantities required tocomplete reaction permits better control over the reaction rate.

                  TABLE 1                                                         ______________________________________                                                       ALCOHOL    TEMPERATURE                                                        ADDED,     TIME OF                                             TIME           (GRAMS)    ADDITION (°C.)                               ______________________________________                                        0 hours        615        70                                                  18 hours       585        20                                                  35 hours       1400       20                                                  39 hours and 10 minutes                                                                      500        30                                                  62 hours and 40 minutes                                                                      1000       78                                                  63 hours and 10 minutes                                                                      104        N/A (not available)                                 ______________________________________                                    

As a result of this reaction, 9.845 kilograms of mixed liquid alkoxideare produced. The alkoxide is analyzed by a spectrographic technique andis found to contain the metallic components set forth in Table 2.

                  TABLE 2                                                         ______________________________________                                                Mg          3.80 wt %                                                         Al          3.49 wt %                                                         Si          9.62 wt %                                                 ______________________________________                                    

A visual inspection of the alkoxide indicates that all of the metalreactants are in solution.

A second reactor is now used to process the alkoxide. The second reactoris a steam jacketed, stainless steel vessel with a volume of 20 gallons.This reactor is provided with a mixer, a thermocouple, an opening tocharge reactants, a vapor outlet opening provided with a condenserpositioned so that condensate is returned to the reactor, and a bottomoutlet to discharge the liquid product.

The 9.845 kilograms of mixed liquid alkoxide are added to the secondreactor containing 7.870 kilograms of ethanol. A mixture of 52.31 gramsof boric acid and 370 grams of ethanol is then added to second reactor.Next, 47.75 grams of phosphoric acid (85%) mixed with 3.160 kilograms,of distilled water and 23.640 kilograms of ethanol are mixed in a tankand then transferred to the second reactor. The second reactor's mixeris operated for 5 minutes to agitate its contents and to effecthydrolysis. The material in the reactor is then allowed to gel andquiescently age for 16 hours. To shear the gel, 20.755 kilograms ofdistilled water is added to the reactor. The contents of the secondreactor are then warmed by operation of the steam jacket and stirredusing the mixer to break up the gel into small particles. During thisstep, the condenser on the outlet of the second reactor which returnscondensate to the reactor is shut off, and a downstream condenser isoperated to remove condensed alcohol and water from the system. Alcoholand water vapors are continuously removed from the reactor bydistillation and replaced with water (Aliquots of water are added to thereactor according to the schedule noted below in Table 3). The neteffect of this removal and replacement is to maintain approximately aconstant liquid volume.

                  TABLE 3                                                         ______________________________________                                                     WATER                                                                         ADDITION,  REACTOR                                               TIME         GRAMS      TEMPERATURE °C.                                ______________________________________                                        0            20,775                                                           0.5 minutes  21,540     78                                                    26.5 minutes 22,460     84                                                    57.7 minutes 10,895     92                                                    1 hour 14.5 minutes                                                                        10,905     93                                                    1 hour 18.5 minutes                                                                         8,880     N/A                                                   1 hour 32.5 minutes                                                                        10,960     93                                                    2 hours 21.5 minutes                                                                       21,875     N/A                                                   4 hours 25.5 minutes                                                                       11,610     95                                                    ______________________________________                                    

The steam for the jacket of the second reactor is then shut off, and theproduct is drained from the bottom outlet of the second reactor into aplastic drum where it is aged at room temperature for 4 days.

After aging, the material in the plastic drum is transferred back to thesecond reactor where it is heated for 41 minutes at 100° C. by steam inthe reactor jacket to remove any remaining alcohol by distillation.After the steam is shut off, the contents of the second reactor arecooled to 68° C., and 11.210 kilograms of distilled water are added.After two hours and 4 minutes, 57.485 kilograms of hydratedmagnesium-aluminum-silicon mixed liquid oxide slurry are removed fromthe reactor, dried in an oven at 100° C., and ball-milled for 1 hour.The chemical composition of the resultant product is analyzed in aninduction coupled argon plasma spectrographic analyzer. The product'scomposition is shown below in Table 4.

                  TABLE 4                                                         ______________________________________                                        MgO                   14.5 wt %                                               Al.sub.2 O.sub.3      15.3 wt %                                               SiO.sub.2             30.4 wt %                                               B.sub.2 O.sub.3       0.67 wt %                                               P.sub.2 O.sub.5       0.71 wt %                                               Loss on Ignition      39.1 wt %                                               ______________________________________                                    

After ball milling, the resultant product is calcined according to thefollowing schedule: Heating from room temperature to 100° C. in hour;Soaking at 100° C. for 1 hour; Heating from 100° to 700° C. at a rate of100° C. per hour; Soaking at 700° C. for two hours; and Cooling to roomtemperature. Following calcination, the product is jet milled to anaverage particulate size of approximately 4μ.

EXAMPLE 2

Using a first reactor similar to that utilized in Example 1, 5.555kilograms of tetraeethylorthosilicate, 350.04 grams of aluminum metal,382.37 grams of magnesium metal, 2.72 grams of iodine, and 1395 grams ofethanol are mixed. This reaction mixture is then heated for severalhours, and, when it reaches 70° C., 1.600 kilograms of ethanol areadded. Upon continued heating, the reactor contents boil violently, andthe exothermic reaction between the alcohol and metals proceeds. Whenthe reactor is at 78° C. after 1 hour and 48 minutes, an additional 800grams of ethanol are added with another 45 grams added 34 minutes afterthat. Twenty two hours and 16 minutes later, 1.745 kilograms of ethanolare added. This reaction proceeds until all of the metal reactants arein solution, and an alkoxide is produced. The chemical composition ofthe alkoxide is then analyzed spectographically and found to have themetallic components shown in Table 5 below.

                  TABLE 5                                                         ______________________________________                                                Mg          4.28 wt %                                                         Al          3.90 wt %                                                         Si          9.11 wt %                                                 ______________________________________                                    

The 8458.64 grams of alkoxide are then mixed with 10.330 kilograms ofethanol in the second reactor used in Example 1. Next, 51.99 grams ofboric acid dissolved in 406.43 grams of ethanol are added to the secondreactor. In a separate tank, 48.49 grams of phosphoric acid (85%), 3.30kilograms of distilled water, and 28.850 kilograms of ethanol are mixedtogether and then added to the reactor. The contents of the reactor aremixed for 5 minutes and then allowed to set and form a gel. After 20hours and 30 minutes of setting, 22.675 kilograms of distilled water areadded to the reactor, and the mixer is used to shear the gel and breakit up into small particles. The composition of the sheared gel is shownin Table 6 below.

                  TABLE 6                                                         ______________________________________                                               MgO          1.27 wt %                                                        Al.sub.2 O.sub.3                                                                           1.21 wt %                                                        SiO.sub.2    4.5 wt %                                                         B.sub.2 O.sub.3                                                                            0.0556 wt %                                                      P.sub.2 O.sub.5                                                                            0.0491 wt %                                               ______________________________________                                    

The remainder of the sheared gel is primarily water and alcohol. Thesteam jacket is then operated to removed alcohol azeotropically from thereactor. During this step, the condensor on the outlet of the secondreactor is shut off, and a downstream condensor is operated to removecondensible alcohol and water vapors from the system. Alcohol and watervapors are continuously removed from the reactor by distillation, duringwhich time aliquots of water are added to the reactor in quantitiesnecessary to maintain approximately a constant volume. The schedule ofwater addition and reactor temperatures are given in Table 7 below.

                  TABLE 7                                                         ______________________________________                                                      WATER                                                                         ADDED,     REACTOR                                              TIME          GRAMS      TEMPERATURE (°C.)                             ______________________________________                                        20 hours 30 minutes                                                                         22,675     N/A                                                  20 hours 48 minutes                                                                         20,895     N/A                                                  20 hours 53 minutes                                                                         11,680     79                                                   21 hours 4 minutes                                                                          22,705     85                                                   21 hours 22 minutes                                                                         11,190     89                                                   21 hours 29 minutes                                                                         10,955     94                                                   21 hours 44 minutes                                                                         10,615     95                                                   21 hours 54 minutes                                                                         11,285     97                                                   22 hours 4 minutes                                                                          11,540     N/A                                                  ______________________________________                                    

The steam jacket heater is then shut down, and the resulting material isallowed to age for 4 days. A chemical analysis of the aged slurryproduct is shown below in Table 8.

                  TABLE 8                                                         ______________________________________                                               MgO          0.60 wt %                                                        Al.sub.2 O.sub.3                                                                           0.58 wt %                                                        SiO.sub.2    1.0 wt %                                                         B.sub.2 O.sub.3                                                                            0.0298 wt %                                                      P.sub.2 O.sub.5                                                                            0.0288 wt %                                               ______________________________________                                    

After aging is completed, the aged material is heated to 94° C. toeffect a final distillation of residual alcohol. During thisdistillation step, 10.290 kilograms of distilled water are added to thesecond reactor. After 2 hours of distillation, 62.259 kilograms ofhydrated magnesium-aluminum-silicon oxide product are withdrawn from thebottom of the reactor and dried in an oven at 100° C. The chemicalanalysis of the hydrated magnesium-aluminum-silicon oxide product priorto drying is shown below in Table 9.

                  TABLE 9                                                         ______________________________________                                               MgO          0.67 wt %                                                        Al.sub.2 O.sub.3                                                                           0.64 wt %                                                        SiO.sub.2    1.23 wt %                                                        B.sub.2 O.sub.3                                                                            0.028 wt %                                                       P.sub.2 O.sub.5                                                                            0.030 wt %                                                ______________________________________                                    

A 1.265 kg sample of the dry product is then ball milled for 4 hours.After ball milling, the sample was chemically analyzed and found to havethe composition shown below in Table 10.

                  TABLE 10                                                        ______________________________________                                                MgO          16.4 wt %                                                        Al.sub.2 O.sub.3                                                                           17.3 wt %                                                        SiO.sub.2    30.7 wt %                                                        B.sub.2 O.sub.3                                                                            0.71 wt %                                                        P.sub.2 O.sub.5                                                                            0.77 wt %                                                ______________________________________                                    

An x-ray diffraction pattern of the sample showed that it was amorphous.According to a scanning electron micrograph of the powder, theagglomerates are comprised of sub-micron particles.

A 103.23 gram sample of dried, unmilled hydratedmagnesium-aluminum-silicon oxide is calcined in an oven according to thefollowing schedule: Heating from room temperature to 700° C. at a rateof 100° C. per hour; Soaking at 700° C. for 4 hours; Heating to 800° C.over the course of an hour; Soaking at 800° C. for 4 hours; and Coolingto room temperature.

An x-ray diffraction pattern of the product indicates that it isamorphous. An infra-red absorption pattern indicates that the sample isamorphous cordierite glass.

A 46.00 gram powder sample of calcined material produced according tothe previous paragraph is again calcined according to the followingschedule: Heating from room temperature to 800° C. at a rate of 200° C.per hour; Heating to 1000° C. over a 2 hour period; Soaking at 1000° C.for 2 hours; and Cooling to room temperature. An x-ray diffractionpattern of the sample indicates that the sample is high (hexagonal)cordierite (2MgO. 2Al₂ O₃.5SiO₂). The infra-red absorption patternindicates that the sample is highly crystalline.

A 2.39 kg portion of the unmilled dried powder was ball milled for 2hours, followed by calcination according to the following schedule:Heating from room temperature to 700° C. at 100° C. per hour; Soaking at700° C. for 18 hours; and Cooling. A chemical analysis of the calcinedpowder is given in Table 11 below.

                  TABLE 11                                                        ______________________________________                                        MgO                   21.0 wt %                                               Al.sub.2 O.sub.3      22.0 wt %                                               SiO.sub.2             38.9 wt %                                               B.sub.2 O.sub.3       0.96 wt %                                               P.sub.2 O.sub.5       0.98 wt %                                               Loss on Ignition      15.9 wt %                                               ______________________________________                                    

An x-ray diffraction pattern indicates that the powder is amorphous.

Four disks of the calcined powder are prepared by pressing the powder ina 11/8 inch die at 30,000 psi. The green density is measured to be 1.16grams per cubic centimeter. After pressing, the disks are heatedaccording to the following schedule to effect sintering: Heating fromroom temperature to 700° C. at a rate of 200° C. per hour; Heating from700° C. to 850° C. at a rate of 100° C. per hour; Soaking at 850° C. forfour hours; and Cooling. The density is measured to be 2.43 grams percubic centimeter or approximately 95% of theoretical density.

EXAMPLE 3

In a first reactor like that used in Example 1, 5.570 kilograms oftetraethylorthosilicate, 1.79 grams of iodine, 354.76 grams of aluminummetal, 381.78 grams of magnesium metal, and 1.075 kilograms of ethanolare mixed and heated to 80° C. After about 17 hours, ethanol is added tothe reactor which is operating at 50° C. according to Table 12 below.

                  TABLE 12                                                        ______________________________________                                        TIME         ETHANOL ADDITION (GRAMS)                                         ______________________________________                                        0            235                                                              1 hour 42 minutes                                                                          265                                                              5 hours 37 minutes                                                                         855                                                              23 hours 42 minutes                                                                        610                                                              31 hours 12 minutes                                                                        2550                                                             ______________________________________                                    

As a result of this reaction, 11.610 kilograms ofmagnesium-aluminum-silicon mixed liquid alkoxide are produced. Theproduct is analyzed by spectrographic techniques and found to have thecomposition shown below in Table 13.

                  TABLE 13                                                        ______________________________________                                                Mg          5.48 wt %                                                         Al          5.73 wt %                                                         Si          14.20 wt %                                                ______________________________________                                    

No visible metal reactants are left after the reaction is completed.

Using a second reactor like that used in Example 1, 10.0186 kilograms ofthe alkoxide are mixed with 6610 kilograms of ethanol and heated to 54°C. A mixture of 46.80 grams of boric acid and 200.12 grams of ethanolare then added to the reactor. In a transfer tank similar to that usedin Example 1, 42.85 grams of phosphoric acid (85%), 2792.81 grams ofdistilled water, and 18.210 kilograms of ethanol are mixed. With thereactor temperature at 58° C., the contents of the transfer tank aremixed with that of the second reactor. The material in the secondreactor is then heated to 78° C. so that it begins to gel. The gel isallowed to age for 2 hours with only the gel in the middle of thereactor being agitated. After 2 hours of aging, 8310.96 grams ofdistilled water is added to the second reactor. The material in thesecond reactor is then aged for 1 hour.

After aging is completed, the contents of the reactor are heated todistill ethanol as described in earlier Examples 1 and 2.

During distilling, water is added according to the schedule shown belowin Table 14.

                  TABLE 14                                                        ______________________________________                                                     WATER                                                                         ADDED      REACTOR                                               TIME         (GRAMS)    TEMPERATURE (°C.)                              ______________________________________                                        20 minutes   10,175     78                                                    27 minutes   10,345     80                                                    37 minutes   11,020     84                                                    46 minutes   11,145     87                                                    57 minutes   11,485     93                                                    1 hour 9 minutes                                                                           11,500     97                                                    ______________________________________                                    

The reactor temperature is then raised to 100° C. and maintained at thattemperature for 15 minutes. The removal of ethanol and water and theaddition of water are then stopped, and 63142.49 grams of material areremoved from the bottom of the reactor. A 277.49 gram portion of theproduct is retained for analysis. Table 15 below shows the compositionof the product.

                  TABLE 15                                                        ______________________________________                                               MgO          0.83 wt %                                                        Al.sub.2 O.sub.3                                                                           0.82 wt %                                                        SiO.sub.2    1.7 wt %                                                         B.sub.2 O.sub.3                                                                            0.0375 wt %                                                      P.sub.2 O.sub.5                                                                            0.0388 wt %                                                      H.sub.2 O    96.8 wt %                                                 ______________________________________                                    

The 62865 gram remainder of the product is dried in an oven andanalyzed. Table 16 below shows the composition of the product.

                  TABLE 16                                                        ______________________________________                                        MgO                   11.9 wt %                                               Al.sub.2 O.sub.3      12.7 wt %                                               SiO.sub.2             25.9 wt %                                               B.sub.2 O.sub.3       .52 wt %                                                P.sub.2 O.sub.5       .55 wt %                                                Loss on Ignition      48.7 wt %                                               ______________________________________                                    

Half of the resulting dry powder is calcined after ball milling for 2hours according to the following schedule: Heating from room temperatureto 500° C. at a rate of 50° C. per hour; Soaking at 500° C. for 2 hours;Heating from 500° C. to 700° C. at a rate of 50° C. per hour; Soaking at700° C. for 4 hours; and Cooling to room temperature. The calcinedpowder is chemically analyzed and found to have the composition shownbelow in Table 17.

                  TABLE 17                                                        ______________________________________                                        MgO                  18.3 wt %                                                Al.sub.2 O.sub.3     19.5 wt %                                                SiO.sub.2            39.9 wt %                                                B.sub.2 O.sub.3      0.78 wt %                                                P.sub.2 O.sub.5      0.83 wt %                                                Loss on Ignition     20.6 wt %                                                ______________________________________                                    

An x-ray diffraction pattern of the calcined powder indicates that thesample is amorphous.

The other half of the dried material is ball milled for 3 hours and thencalcined. Calcination is effected according to the following schedule:Heating from room temperature to 500° C. at a rate of 50° C. per hour;Soaking at 500° C. for 2 hours; Raising the temperature from 500° C. to700° C. at 50° C. per hour; Soaking at 700° C. for 4 hours; and Coolingto room temperature. An x-ray diffraction pattern indicates that thepowder is amorphous.

The calcined powder is mixed together and then jet milled. The jetmilled powder is then pressed into 11/8" inch diameter disks with apressure of 30,000 psi. The disks are then sintered according to thefollowing schedule: Heating from room temperature to 950° C. at a rateof 100° C.; Soaking at 950° C. for 4 hours; and Cooling to roomtemperature. The density of the disk is measured to be 2.50 grams percubic centimeter.

EXAMPLE 4

Powder is prepared substantially according to the procedure described inExample 1. After calcining to 700° C., and jet milling, the powder isanalyzed and found to have the composition shown below in Table 18.

                  TABLE 18                                                        ______________________________________                                               MgO          20.3 wt %                                                        Al.sub.2 O.sub.3                                                                           21.6 wt %                                                        SiO.sub.2    40.7 wt %                                                        B.sub.2 O.sub.3                                                                            0.83 wt %                                                        P.sub.2 O.sub.5                                                                            0.88 wt %                                                        LOI          15.9 wt %                                                 ______________________________________                                    

An x-ray diffraction pattern indicates that it is amorphous. Disks of11/8" diameter, each weighing 3 grams, are pressed using a pressure of30,000 psi. The green densities of the disks are given below in Table19.

                  TABLE 19                                                        ______________________________________                                                   GREEN DENSITY GRAMS                                                DISK #     PER CUBIC CENTIMETER                                               ______________________________________                                        1          1.25                                                               2          1.19                                                               3          1.22                                                               4          1.24                                                               5          1.24                                                               6          1.20                                                               ______________________________________                                    

Disks 1 and 2 are sintered at 875° C. according to the followingschedule: Heating from room temperature to 700° C. at 150° C. per hour;Heating from 700° to 875° C. at 100° C. per hour; Soaking at 875° C. for2 hours; and Cooling. An x-ray diffraction of a monolithic part of onedisk indicates that it is comprised of high (hexagonal) cordierite. Theother disk is ground into a powder. The ground material is analyzed andfound to have an infra-red absorption pattern which indicates that it iscrystalline cordierite. An x-ray diffraction pattern indicates that itis high (hexagonal) cordierite. The density is measured to be 2.50 gramsper cubic centimeter.

Disks 3 and 4 are sintered to 850° C. according to the followingschedule: Heating from room temperature to 700° C. at 150° C. per hour;Heating from 700° to 850° C. at 100° C. per hour; Soaking at 850° C. fortwo hours; and Cooling. An x-ray diffraction pattern of a monolithicportion of a disk indicates that it is amorphous. The disks arere-calcined to 825° C. at 100° C. per hour, and allowed to cool. Anx-ray diffraction pattern of a ground portion of the disk indicates thatit is amorphous. An infra-red absorption pattern indicates that thepowder is amorphous. Density is measured to be 2.44 grams per cubiccentimeter.

Disks 5 and 6 are sintered to 825° C. according to the followingschedule: Increasing the temperature from room temperature to 825° C. at100° C. per hour; Soaking at 825° C. for two hours; and Cooling. Anx-ray diffraction pattern of each disk indicates that it is amorphous.

EXAMPLE 5

263 grams of calcined, milled powder prepared substantially according tothe procedure outlined in Example 1 is re-calcined to 800° C. accordingto the following schedule: Heating from room temperature to 500° C. at100° C. per hour; Soaking at 500° C. for 3 hours; Heating from 500° to800° C. at 100° C. per hour; Soaking at 800° C. for 2 hours; andCooling. The powder is dry ball milled for 1 hour and pressed into a11/8" diameter, 2 gram disk at 30,000 psi. The disk is sintered at 850°C. according to the following schedule: Heating from room temperature to700° C. at 100° C. per hour; Soaking at 700° C. for 1 hour; Heating from700° to 825° C. at 100° C. per hour; Soaking at 825° C. for 3 hours;Heating from 825° to 850° C. at 100° C. per hour; Soaking at 850° C. for4 hours; and Cooling. The density of the disk is measured to be 2.55grams per cubic centimeter, while an infra-red absorption patternindicates that it is amorphous.

Three disks prepared as described above and sintered to 850° C. arere-sintered to 875° C. according to the following schedule: Heating fromroom temperature to 875° C. at 150° C. per hour; Soaking at 875° C. for2 hours; and Cooling. An x-ray diffraction pattern indicates that thedisks are high (hexagonal) cordierite.

Although the invention has been described in detail for the purpose ofillustration, it is understood that such detail is solely for thatpurpose, and variations can be made therein by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed:
 1. A stable, homogeneous mixed liquid alkoxidecomprising:a magnesium metal alkoxide; an aluminum metal alkoxide; asilicon tetraalkoxide; wherein the molar ratio of magnesium alkoxide toaluminum alkoxide is greater than 1:2.
 2. A stable, mixed liquidalkoxide according to claim 1, wherein said alkoxide is an ethoxide.